In general, a construction machine such as an excavator includes a plurality of actuators for travelling or driving various working apparatuses and the plurality of actuators are driven by a working fluid discharged from a variable displacement type hydraulic pump driven by an engine or an electric motor.
The flow of the working fluid discharged from the variable displacement type hydraulic pump is controlled depending on a working load to minimize power loss and one example thereof is shown in FIG. 1.
Referring to FIG. 1, a swash plate angle is controlled according to a signal pressure inputted into a regulator 2, and as a result, the discharge flow of the hydraulic pump 1 driven with being directly connected to the engine is controlled. The signal pressure inputted into the regulator 2 is drawn out from a center bypass line 6 passing through a plurality of control valves 3 and a relief valve 4 and an orifice 5 are connected to the center bypass line 6 in parallel to each other.
An operation procedure of the hydraulic pump controlling apparatus having the above-mentioned configuration will be hereinafter described. First, when an operation signal of a control unit such as a joystick is not inputted, the plurality of control valves 3 are positioned in a neutral state. In such a state, a working fluid discharged from the hydraulic pump 1 is discharged to a tank T through the center bypass line 6. At this time, the flow of the working fluid drained to the tank T through the orifice 5 is limited to allow the pressure of the center bypass line 6 to increase up to a relief pressure of the relief valve 4 and the increased pressure is inputted into the regulator 2 to reduce the flow of the hydraulic pump 1 by controlling a swash plate angle of the hydraulic pump 1.
On the contrary, when the control signal is inputted from the control unit, any one of the plurality of control valves 3 is switched, and as a result, the flow of the working fluid that flows through the center bypass line 6 decreases. Therefore, the magnitude of the signal pressure inputted into the regulator 2 decreases, and as a result, the swash plate angle of the hydraulic pump 1 is controlled to increase the flow of the hydraulic pump 1.
According to the hydraulic pump controlling apparatus, even when a working apparatus or a travelling apparatus is not driven, the hydraulic pump 1 should discharge a predetermined flow so that the working fluid of the center bypass line 6 reaches the relief pressure of the relief valve 4. That is, even when the plurality of control valves 3 are all in the neutral state, the hydraulic pump 1 should be driven to supply the predetermined flow to cause the power of the engine to be lost.
Further, since the working fluid discharged from the hydraulic pump 1 is drained to the drain tank T through the orifice 5 and the relief valve 4, the pressure is lost, and as a result, the loss of the power of the engine E further increases and the temperature of the working fluid rises. When the temperature of the working fluid rises, driving precision of each actuator deteriorates and high-price hydraulic components are damaged to shorten a life-span, thereby deteriorating reliability of the construction machine.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.